DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 871 



autumn when swarms of little gurnards are captured, the smallest of which are very little 

 larger than those reared in the laboratory, while others are three or four times longer. 



Moreover, experience of fishes such as the salmon, in which all the ova issue nearly 

 simultaneously, shows us that the growth of the young of the same fish is variable, many 

 being larger than others at a given time ; some, for instance, becoming smolts at the end 

 of the first year, others not till the end of the second. Further, during the second year 

 great disparity occasionally exists amongst the young fishes. 



When we come to survey the condition in the cod, the problem is more complex, since 

 the material is less abundant and more difficult to obtain. Statements had been made 

 by various authors about the life-history of the cod, but these were both vague and 

 incomplete; Prof. G. 0. Sars, indeed, as already indicated (p. 153), was the first to 

 produce a definite and satisfactory account of certain stages. He, however, found, no 

 intermediate links between the larval form of 6 mm. and the post-larval form 24 mm. in 

 length, the former occurring on 28th May, the latter on 12th June, and the most recent 

 remarks of Ryder leave the same gap. The spawning period of the cod, therefore, would 

 appear to be later in the Norwegian waters. It occurs as a rule in April in the British 

 seas, though a margin must be given on both sides of this period,* and the larval cod 

 abound in the surface-waters in areas frequented by the adults at the time. Towards the 

 end of the same month, however, small Gadoids occur in St Andrews Bay, the least being 

 about 6 mm., so that it is possible such represent a post-larval stage from early ova. 

 Others again are double the length and upward, indeed there is great variety. These 

 small forms are met with amongst the others throughout the summer, and generally occur 

 in the mid- water net rather than in the trawl. On the 1st of June, however, the dis- 

 tinctive coloration of the young cod (now ^-| in. in length) is recognised, in a rudimentary 

 condition, and subsequently there is no difficulty in following it. They occur in the 

 trawl, and at the margin of the tidal rocks.t Now, can we assert that all these are the 

 young produced from the ova of cod which spawn in April? At first one of us was 

 disposed to think that those which appear in shoals off the rocks in June, and which are 

 about an inch in length, were those of the previous season, since it would be difficult to 

 explain this remarkable rapidity of growth if the spawning period (viz., April) be correctly 

 stated. Though the latter rests on proved observation, yet it must be borne in mind 

 that the limitation of the spawning period to April is arbitrary, and it may only reach its 

 culminating point then. This consideration, and the remarks formerly made as to the 

 causes of variability in size, may, when coupled with great rapidity in growth, form the 

 whole into one continuous series of young cod of the season. Such has been rendered 

 more probable by the occurrence of the smaller forms early in April as well as subse- 

 quently. Moreover, a change of area apparently takes place to some extent, since the 

 mid-water net shows that these post-larval cod only appear in the Bay in April and May. 



* Vide "The Pelagic Fauna of St Andrews Bay," Seventh Annual Report of the Fishery Board for Scotland. 

 f As shown in the Report on the Pelagic Fauna, the sizes of the pelagic young-food fishes captured in the mid-water 

 net does not increase as the season advances, apparently for the reason that the large forms go downwards as they grow. 



